SSL test programs: allow for test hooks init and error reports

Create utility functions to set up test hooks and report errors that
the test hooks might detect. Call them in ssl_client2 and ssl_server2.

Test hooks are potentially enabled by compiling with
MBEDTLS_TEST_HOOKS.

This commit only sets up the functions. It doesn't make them do
anything yet.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 08317b5..c04f47a 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -1369,6 +1369,8 @@
 #endif  /* MBEDTLS_MEMORY_DEBUG */
 #endif  /* MBEDTLS_MEMORY_BUFFER_ALLOC_C */
 
+    test_hooks_init( );
+
     /*
      * Make sure memory references are valid in case we exit early.
      */
@@ -3998,6 +4000,14 @@
     mbedtls_free( context_buf );
 #endif
 
+    if( test_hooks_failure_detected( ) )
+    {
+        if( ret == 0 )
+            ret = 1;
+        mbedtls_printf( "Test hooks detected errors.\n" );
+    }
+    test_hooks_free( );
+
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
 #if defined(MBEDTLS_MEMORY_DEBUG)
     mbedtls_memory_buffer_alloc_status();